The 69-year-old cattle farmer has been making this journey several times a week for almost a year. Yamamoto is one of about 10 farmers from Namie who are defying government orders to euthanise their cattle, their market value obliterated by ingestion of radioactive caesium.

Nothing, he says, will stop him from carrying out what is almost certain to be the last duty of care to animals that have been his family's livelihood for generations. Not the nuclear contamination that has made his hometown of Namie uninhabitable; nor the piercing cold that blankets his farm on this winter afternoon. And definitely not the officials who dismiss his compassion as hopelessly misplaced.

Almost a year since the Fukushima Daiichi accident turned 930 square miles of land into a no-go zone, birdsong and the laboured groans of his 36 black-haired wagyu cows – animals once highly prized for their premium-quality beef – are the only signs of life near the farmhouse he once shared with his family.

Yamamoto, who obtained a permit allowing him to enter the nuclear evacuation zone to feed his animals, agreed to take the Guardian on a brief visit to his farm, which is 14km from the plant.

His route takes him past fields strewn with tsunami wreckage, still untouched, and through the centre of Namie, a town of that once housed 22,000 people but now lies abandoned.

Warnings about the imminent arrival of Fukushima Daiichi's toxic payload drove every last resident from their homes, and forced farmers to condemn their animals to slow, painful deaths from starvation.

The nuclear accident has inflicted serious damage to brand Fukushima and its annual $3.2bn (£1.57bn) farming industry, but Yamamoto refuses to believe that all is lost.

"I left like everyone else after 11 March," he said. "I couldn't stop worrying about my cows, so I started coming back in every other day to feed them." The round-trip from his temporary accommodation took six hours.

In May, the then prime minister, Naoto Kan, ordered the killing of livestock by lethal injection after radiation made them commercially worthless. Local farmers say the operation has been blighted by mishaps, including the escape of an estimated 1,000 cattle from their homesteads, and conflicting data on how many cows have been killed.

"Straight after the disaster, my cows had nothing to eat or drink ... many of them starved to death right where they were tethered," Yamamoto said. "I had to decide whether to leave the ones still alive or keep them healthy, even though we were separated."

But time could be running out for the animals whose survival has turned into a personal mission. In the year since the disaster, Yamamoto says he has not received any feed from the government; what little he has came from private donors, including farmers in Australia after they were approached by the country's meat and livestock office in Tokyo.

"Eventually the feed will run out, and the government has said it will kill every last cow," says Yamamoto, whose cows once fetched well over $10,000 per head. "But that is something I can't allow to happen. "I could never kill these cows. They are like members of my family."

He is pinning his hopes on studies being conducted by academics to gauge the level of contamination in livestock. "No one has said for sure if cows that eat and drink in Fukushima really are beyond help," he said. "We want someone to conduct a proper study."

"We accept that the meat will never go on sale, but the cows could be put to some other commercial use," says Ryoichi Harada, another rebel farmer who helps Yamamoto feed his animals.

As he leaves Namie at dusk, Yamamoto passes the entrance to another farm, the black figures of wagyu cows just visible on a distant ridge. At the entrance, animal skulls have been placed next to signs demanding that the authorities end the euthanasia programme.

The site has been hastily renamed Hope Farm, but in Yamamoto's voice there is only despair: "Japan is supposed to be an advanced nation, so how is it that we have forgotten to care for our animals?"